1. Field of the Invention
The present invention relates to a method of manufacturing a stamper for producing optical discs, which method comprises the application of a photoresist film to a substrate and the subsequent structuring of said photoresist film by exposing and developing said photoresist film. The present invention furthermore relates to a stamper thus obtained and to an optical disc obtained by means of such a stamper.
2. Description of Related Art
A method of this kind is known from Dutch patent application no. 9400225. According to the method of manufacturing a stamper disclosed therein, a stamper plate is subjected to a pre-treatment consisting of a cleaning step and the possible application of a primer for the photoresist to be applied. Then a negative-effect photoresist is coated onto the pre-treated stamper plate, which photoresist is then dried so as to obtain a photoresist film. In a subsequent step, the photoresist film that has been coated onto the stamper plate is selectively exposed to laser light. By selectively exposing the negative-effect photoresist, an acid is formed in the exposed areas, after which a heating step is carried out, as a result of which the photoresist in the exposed areas will be crosslinked whilst catalysis of the acid takes place. Then the selectively exposed, coated photoresist is integrally exposed, as a result of which an acid is formed in the non-exposed areas as well, which acid causes the areas which have not been selectively exposed, and which are not crosslinked, therefore, to dissolve more quickly during the developing step. After said selective exposure, the integrally exposed, coated photoresist film is developed for the purpose of obtaining the structured photoresist film. The exposed areas of a negative photoresist film thus remain after the developing step, whilst non-exposed areas are removed by means of a developing process. Then an additional exposure step in the deep UV range and a heating step at a high temperature (hard bake) are carried out in order to strengthen the exposed and thus crosslinked areas additionally by further crosslinking of polymer chains. A stamper obtained by using such a method comprises a nickel shell provided with photoresist posts. Due to dimensional stability deficiencies of the photoresist posts, stamper thus formed, which is used in the mould of an injection moulding machine for mass-producing CD replicas, has a limited life. Signal measurements in combination with transmission order measurements on the CD replicas thus produced indicate that the post geometries on the stamper had deteriorated to an unacceptable degree after about 5,000 replicas, which has an adverse effect on the signal quality.